The current radio communication system uses the IMT 2000 standard which realizes data rates of 144 kbps in the mobile environment and 2 Mbps in the stationary environment.
However, a higher-rate radio system is required so as to realize multimedia communication such as e-mail, high-rate Internet access, transmission of high-precision moving pictures, and downloads of huge volumes of files in the mobile environment. Recently, 3.5th and 4th generation radio communication studies have been progressing, which aim at the data rates of 5 Mbps at a maximum in the mobile condition and several tens of Mbps in the stationary condition.
In order to realize high-rate and high-quality information transmission in the radio communication environment, transmission methods with strong characteristics against deterioration of communication quality and high frequency allowance are needed, which include Orthogonal Frequency Division Multiplex (OFDM) and the Multi-Carrier-Code Division Multiple Access (MC-CDMA) systems.
The OFDM scheme for applying a plurality of orthogonal carriers to the CDMA scheme to thus realize multiplexing is classified as the OFDM Time Division Multiple Access (OFDM-TDMA) for allowing a plurality of users to use different time slots as shown in FIG. 1, and the OFDM Frequency Division Multiple Access (OFDM-FDMA) for allowing different users to use predetermined carriers as shown in FIG. 2.
The MC-CDMA, categorized as the CDMA schemes, loads user information on different carriers and provides the same to the frequency domain so that a plurality of users may perform communication through code multiplexing as shown in FIG. 3.
However, the above-described OFDM scheme is weak in interference generated by other cells in the multi-cell environment, and hence, the bit error rate (BER) and communication capacity are problematically worsened because of the interference, and the above-noted MC-CDMA scheme is strong against interference provided by other cells but inter-code interference is increased to worsen system performance when the number of users in a cell is increased, and the same is weak in the peak to average power ratio (PAPR).